OCaml support: Add OCaml support in xgettext.

OCaml support: Add OCaml support in xgettext.

* gettext-tools/doc/lang-ocaml.texi: New file.
* gettext-tools/doc/Makefile.am (gettext_TEXINFOS): Add it.
* gettext-tools/doc/gettext.texi (No string concatenation): Mention string
concatenation in OCaml.
(List of Programming Languages): Include lang-ocaml.texi.
* gettext-tools/doc/xgettext.texi: Document the -L OCaml option.
* gettext-tools/src/x-ocaml.h: New file.
* gettext-tools/src/x-ocaml.c: New file.
* gettext-tools/src/xgettext.c: Include x-ocaml.h.
(flag_table_ocaml): New variable.
(main): Invoke init_flag_table_ocaml, x_ocaml_extract_all, x_ocaml_keyword.
(usage): Document the -L OCaml option.
(language_to_extractor, extension_to_language): Support OCaml.
* gettext-tools/src/FILES: Mention x-ocaml.h, x-ocaml.c.
* gettext-tools/src/Makefile.am (noinst_HEADERS): Add x-ocaml.h.
(xgettext_SOURCES): Add x-ocaml.c.
* gettext-tools/po/POTFILES.in: Add src/x-ocaml.c.